For small groups, I don't bother using any utility skills. Couple of dodges to stack bleeds, and skills 1-3 finish them off. For large groups, I use all of my utilities, and LDB 3-4 times in a row. Melts through large groups like butter.

The absolute limit I've been able to achieve was 2 veterans and 3 normal mobs all at once.

Steelseries Sensei is a good option, but it only has 4 side buttons. 5 if you include mouse wheel click.
Cyborg RAT/MMO 7 are also decent options. The MMO 7 comes with a mini D-pad (4 buttons + press down the Dpad for 1 more). RAT7 doesn't have that feature, but it still has plenty of buttons.